1. Field of the Invention
The present invention relates to a heat-assisted magnetic recording head for use in heat-assisted magnetic recording where a magnetic recording medium is irradiated with near-field light to lower the coercivity of the magnetic recording medium for data recording, and to a head gimbal assembly and a magnetic recording device each of which includes the heat-assisted magnetic recording head.
2. Description of the Related Art
Recently, magnetic recording devices such as a magnetic disk drive have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a reproducing head including a magnetoresistive element (hereinafter, also referred to as MR element) intended for reading and a recording head including an induction-type electromagnetic transducer intended for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
Magnetic recording media are discrete media each made of an aggregate of magnetic fine particles, each magnetic fine particle forming a single-domain structure. A single recording bit of a magnetic recording medium is composed of a plurality of magnetic fine particles. For improved recording density, it is necessary to reduce asperities at the borders between adjoining recording bits. To achieve this, the magnetic fine particles must be made smaller. However, making the magnetic fine particles smaller causes the problem that the thermal stability of magnetization of the magnetic fine particles decreases with decreasing volume of the magnetic fine particles. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic recording medium, and this makes it difficult to perform data recording with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technique so-called heat-assisted magnetic recording. This technique uses a magnetic recording medium having high coercivity. When recording data, a magnetic field and heat are simultaneously applied to the area of the magnetic recording medium where to record data, so that the area rises in temperature and drops in coercivity for data recording. Hereinafter, a magnetic head for use in heat-assisted magnetic recording will be referred to as a heat-assisted magnetic recording head.
In heat-assisted magnetic recording, near-field light is typically used as a means for applying heat to the magnetic recording medium. A commonly known method for generating near-field light is to use a near-field optical probe or so-called plasmon antenna, which is a piece of metal that generates near-field light from plasmons excited by irradiation with light.
In general, laser light that is used for generating near-field light is guided through a waveguide that is provided in the slider to the plasmon antenna that is located near the medium facing surface of the slider. Possible techniques of placement of a light source that emits the laser light are broadly classified into the following two. A first technique is to place the light source away from the slider. A second technique is to fix the light source to the slider.
The first technique is described in JP 2007-200475 A, for example. The second technique is described in U.S. Patent Application Publication No. 2008/0002298 A1 and U.S. Patent Application Publication No. 2008/0043360 A1, for example.
The first technique requires an optical path of extended length including such optical elements as a mirror, lens, and optical fiber in order to guide the light from the light source to the waveguide. This causes the problem of increasing energy loss of the light in the path. The second technique is free from the foregoing problem since the optical path for guiding the light from the light source to the waveguide is short.
The second technique, however, has the following problem. Hereinafter, the problem that can occur with the second technique will be described in detail. The second technique typically uses a laser diode as the light source. The laser diodes available include edge-emitting laser diodes and surface-emitting laser diodes. In an edge-emitting laser diode, the emission part for emitting the laser light is located in an end face that lies at an end of the laser diode in a direction parallel to the plane of an active layer. The emission part emits the laser light in the direction parallel to the plane of the active layer. In a surface-emitting laser diode, the emission part for emitting the laser light is located in a surface that lies at an end of the laser diode in a direction perpendicular to the plane of the active layer. The emission part emits the laser light in the direction perpendicular to the plane of the active layer.
The laser light emitted from a laser diode can be made incident on the waveguide by a technique described in U.S. Patent Application Publication No. 2008/0002298 A1, for example. This publication describes arranging a surface-emitting laser diode with its emission part opposed to the surface of the slider on the trailing side so that the laser light emitted from the emission part is incident on the waveguide from above. Surface-emitting laser diodes, however, typically have a lower optical output as compared with edge-emitting laser diodes. The technique therefore has the problem that it is difficult to provide laser light of sufficiently high intensity for use in generating near-field light.
The laser light emitted from a laser diode may be made incident on the waveguide by other techniques. For example, U.S. Patent Application Publication No. 2008/0043360 A1 describes a technique in which the incident end face of the waveguide is arranged at the surface opposite to the medium facing surface of the slider, and the laser diode is arranged with its emission part opposed to this incident end face so that the laser light emitted from the emission part is incident on the incident end face of the waveguide without the intervention of any optical element. This technique allows the use of an edge-emitting laser diode which has a high optical output. However, this technique has the problem that it is difficult to align the emission part of the laser diode with respect to the incident end face of the waveguide with high precision, since the position of the emission part of the laser diode can vary within a plane perpendicular to the optical axis of the waveguide.
To cope with this, the edge-emitting laser diode may be fixed to the top surface of the slider that lies at an end of the slider above the top surface of the substrate, so that the laser light is emitted in a direction parallel to the top surface of the slider, while arranging the waveguide so that the incident end face of the waveguide is opposed to the emission part of the laser diode. Here, the outer surface of the waveguide, excluding the incident end face and the bottom surface, is covered with an overcoat layer that also functions as a clad layer. An end face of the overcoat layer is formed around the incident end face of the waveguide. To manufacture a heat-assisted magnetic recording head of such a configuration, the laser diode is installed so that the emitting end face of the laser diode including the emission part faces the incident end face of the waveguide and the end face of the overcoat layer. Hereinafter, a description will be given of problems that can occur when manufacturing the heat-assisted magnetic recording head of such a configuration.
When manufacturing the heat-assisted magnetic recording head of the foregoing configuration, the laser diode is ideally installed so that the emitting end face of the laser diode comes into contact with the incident end face of the waveguide and the end face of the overcoat layer. In view of the installation accuracy of the laser diode, however, it is actually difficult to install the laser diode so that the emitting end face of the laser diode is in contact with the incident end face of the waveguide and the end face of the overcoat layer. Actually, a gap on the order of several micrometers is formed between the emitting end face of the laser diode and each of the incident end face of the waveguide and the end face of the overcoat layer. Such a gap extends over a long distance greater than or equal to 100 μm, which is the width of the end face of the laser diode.
To manufacture the heat-assisted magnetic recording head of the foregoing configuration, the slider is subjected to a machining process including polishing of the medium facing surface and fabrication of the flying rails, after the laser diode is installed as described above. Subsequently, the heat-assisted magnetic recording head is subjected to a cleaning process. During the machining process on the slider, foreign substances such as polishing slurry and chippings may get into the gap between the emitting end face of the laser diode and each of the incident end face of the waveguide and the end face of the overcoat layer. The foreign substances caught in the gap cannot easily be removed by the cleaning process. If foreign substances are present in the gap, some of the laser light that is emitted from the laser diode and supposed to be incident on the waveguide may be scattered by the foreign substances and fail to be incident on the waveguide. This causes the problem of a drop in the intensity of the laser light for use for generating near-field light.
To prevent the occurrence of the foregoing problem, the gap may be sealed with resin after the installation of the laser diode, before the machining process on the slider. Since the gap of around several micrometers extends over a long distance of 100 μm or more as mentioned above, however, it is not easy for the resin to get into the gap. As a result, the filling status of the gap with the resin can vary product by product, which causes the problem of variations in quality.